The invention relates to a circuit arrangement in which a switching transistor controls the energisation and de-energisation process of a coil. This type of circuit arrangement is used, for example, as a transistor ignition circuit in Otto cycle engines.
With the known transistor ignition circuits high voltage power transistors or Darlington transistors are used as switches in order to control the ignition coil. Triggering of switching transistors takes place for example by means of interrupter contacts, Reed contacts, field plates, inductive generators or by means of optoelectronic arrangements. In order to protect the switching transistor from high back voltage impulses when the interrupter contact is opened, the rise in the primary voltage of the ignition coil is delayed by means of a protective capacitor which is connected in parallel to the emitter-collector path of the switching transistor. Moreover avalanche diodes are connected as protective diodes parallel to the emitter-collector path or, better still, parallel to the base-collector path of the switching transistor, in order to avoid the switching transistor being operated in the avalanche region during interruptions in operation.